Systems and methods for flyback power converters with switching frequency and peak current adjustments

ABSTRACT

System and method for regulating a power converter. The system includes a comparator configured to receive a first signal and a second signal and generate a comparison signal based on at least information associated with the first signal and the second signal. The first signal is associated with at least an output current of a power converter. Additionally, the system includes a pulse-width-modulation generator configured to receive at least the comparison signal and generate a modulation signal based on at least information associated with the comparison signal, and a driver component configured to receive the modulation signal and output a drive signal to a switch to adjust a primary current flowing through a primary winding of the power converter. The modulation signal is associated with a modulation frequency corresponding to a modulation period.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/376,290, filed Dec. 12, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/293,280, filed Jun. 2, 2014, which is acontinuation of U.S. patent application Ser. No. 13/164,608, filed Jun.20, 2011, which claims priority to Chinese Patent Application No.201110144768.2, filed May 23, 2011, all of these applications beingincorporated by reference herein for all purposes.

Additionally, U.S. patent application Ser. Nos. 12/859,138 and13/052,869 are incorporated by reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides switching frequency and peakcurrent adjustments in response to loading changes. Merely by way ofexample, the invention has been applied to a flyback power converter.But it would be recognized that the invention has a much broader rangeof applicability.

Generally, a conventional power conversion system often uses atransformer to isolate the input voltage on the primary side and theoutput voltage on the secondary side. To regulate the output voltage,certain components, such as TL431 and an opto-coupler, can be used totransmit a feedback signal from the secondary side to a controller chipon the primary side. Alternatively, the output voltage on the secondaryside can be imaged to the primary side, so the output voltage iscontrolled by directly adjusting some parameters on the primary side.

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system with primary-side sensing and regulation. The powerconversion system 100 includes a primary winding 110, a secondarywinding 112, an auxiliary winding 114, a power switch 120, a currentsensing resistor 130, an equivalent resistor 140 for an output cable,resistors 150 and 152, and a rectifying diode 160. For example, thepower switch 120 is a bipolar transistor. In another example, the powerswitch 120 is a MOS transistor.

To regulate the output voltage within a predetermined range, informationrelated to the output voltage and the output loading often needs to beextracted. In the power conversion system 100, such information can beextracted through the auxiliary winding 114. When the power switch 120is turned on, the energy is stored in the secondary winding 112. Then,when the power switch 120 is turned off, the stored energy is releasedto the output terminal, and the voltage of the auxiliary winding 114maps the output voltage on the secondary side as shown below.

$\begin{matrix}{V_{FB} = {{\frac{R_{2}}{R_{1} + R_{2}} \times V_{aux}} = {k \times n \times \left( {V_{o} + V_{F} + {I_{o} \times R_{eq}}} \right)}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where V_(FB) represents a voltage at a node 154, and V_(aux) representsthe voltage of the auxiliary winding 114. R₁ and R₂ represent theresistance values of the resistors 150 and 152 respectively.Additionally, n represents a turns ratio between the auxiliary winding114 and the secondary winding 112. Specifically, n is equal to thenumber of turns of the auxiliary winding 114 divided by the number ofturns of the secondary winding 112. V_(o) and I_(o) represent the outputvoltage and the output current respectively. Moreover, V_(F) representsthe forward voltage of the rectifying diode 160, and R_(eq) representsthe resistance value of the equivalent resistor 140. Also, k representsa feedback coefficient as shown below:

$\begin{matrix}{k = \frac{R_{2}}{R_{1} + R_{2}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

FIG. 2 is a simplified diagram showing a conventional operationmechanism for the flyback power conversion system 100. As shown in FIG.2, the controller chip of the conversion system 100 uses asample-and-hold mechanism. When the demagnetization process on thesecondary side is almost completed and the current I_(sec), of thesecondary winding 112 almost becomes zero, the voltage V_(aux) of theauxiliary winding 112 is sampled at, for example, point A of FIG. 2. Thesampled voltage value is usually held until the next voltage sampling isperformed. Through a negative feedback loop, the sampled voltage valuecan become equal to a reference voltage V_(ref). Therefore,

V _(FB) =V _(ref)  (Equation 3)

Combining Equations 1 and 3, the following can be obtained:

$\begin{matrix}{V_{o} = {\frac{V_{ref}}{k \times n} - V_{F} - {I_{o} \times R_{eq}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

Based on Equation 4, the output voltage decreases with the increasingoutput current.

But the power conversion system 100 often cannot provide effectiveresponse to output loading changes. Hence it is highly desirable toimprove the techniques of primary-side sensing and regulation.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides switching frequency and peakcurrent adjustments in response to loading changes. Merely by way ofexample, the invention has been applied to a flyback power converter.But it would be recognized that the invention has a much broader rangeof applicability.

According to one embodiment, a system for regulating a power converterincludes a comparator configured to receive a first signal and a secondsignal and generate a comparison signal based on at least informationassociated with the first signal and the second signal. The first signalis associated with at least an output current of a power converter.Additionally, the system includes a pulse-width-modulation generatorconfigured to receive at least the comparison signal and generate amodulation signal based on at least information associated with thecomparison signal, and a driver component configured to receive themodulation signal and output a drive signal to a switch to adjust aprimary current flowing through a primary winding of the powerconverter. The modulation signal is associated with a modulationfrequency corresponding to a modulation period. The modulation frequencyincreases with the output current at a first slope within a firstcurrent range, the modulation frequency increases with the outputcurrent at a second slope within a second current range, and themodulation frequency increases with the output current at a third slopewithin a third current range. The first current range and the thirdcurrent range are separated by at least the second current range, andeach of the first slope, the second slope, and the third slope is largerthan zero. The primary current is associated with a peak magnitude foreach modulation period. The peak magnitude remains constant or increaseswith respect to the output current at a fourth slope within a fourthcurrent range, and the fourth slope is equal to or larger than zero. Thepeak magnitude increases with the output current at a fifth slope withina fifth current range, and the fifth slope is larger than zero. The peakmagnitude remains constant or increases with respect to the outputcurrent at a sixth slope within a sixth current range, and the sixthslope is equal to or larger than zero. The fourth current range and thesixth current range are separated by at least the fifth current range.

According to another embodiment, a method for regulating a powerconverter includes receiving a first signal and a second signal. Thefirst signal is associated with at least an output current of a powerconverter. Additionally, the method includes processing informationassociated with the first signal and the second signal, generating acomparison signal based on at least information associated with thefirst signal and the second signal, receiving at least the comparisonsignal, and generating a modulation signal based on at least informationassociated with the comparison signal. Moreover, the method includesreceiving the modulation signal, and outputting a drive signal based onat least at least information associated with the modulation signal toadjust a primary current flowing through a primary winding of the powerconverter. The modulation signal is associated with a modulationfrequency corresponding to a modulation period. The modulation frequencyincreases with the output current at a first slope within a firstcurrent range, the modulation frequency increases with the outputcurrent at a second slope within a second current range, and themodulation frequency increases with the output current at a third slopewithin a third current range. The first current range and the thirdcurrent range are separated by at least the second current range, andeach of the first slope, the second slope, and the third slope is largerthan zero. The primary current is associated with a peak magnitude foreach modulation period. The peak magnitude remains constant or increaseswith respect to the output current at a fourth slope within a fourthcurrent range, and the fourth slope is equal to or larger than zero. Thepeak magnitude increases with the output current at a fifth slope withina fifth current range, and the fifth slope is larger than zero. The peakmagnitude remains constant or increases with respect to the outputcurrent at a sixth slope within a sixth current range, and the sixthslope is equal to or larger than zero. The fourth current range and thesixth current range are separated by at least the fifth current range.

According to yet another embodiment, a system for regulating a powerconverter includes a first comparator configured to receive a firstsignal and a second signal and generate a first comparison signal basedon at least information associated with the first signal and the secondsignal. The first signal is associated with at least an output currentof a power converter. Additionally, the system includes a secondcomparator configured to receive a third signal and a fourth signal andgenerate a second comparison signal based on at least informationassociated with the third signal and the fourth signal. The third signalis related to the second signal, and the fourth signal is associatedwith a primary current flowing through a primary winding of the powerconverter. Moreover, the system includes a logic component configured toreceive at least the second comparison signal and generate a logicsignal based on at least information associated with the secondcomparison signal, a pulse-width-modulation generator configured toreceive at least the first comparison signal and the logic signal andgenerate a modulation signal based on at least information associatedwith the first comparison signal and the logic signal, and a drivercomponent configured to receive the modulation signal and output a drivesignal to a switch to adjust the primary current.

According to yet another embodiment, a method for regulating a powerconverter includes receiving a first signal and a second signal, and thefirst signal is associated with at least an output current of a powerconverter. Additionally, the method includes processing informationassociated with the first signal and the second signal, generating afirst comparison signal based on at least information associated withthe first signal and the second signal, and receiving a third signal anda fourth signal, the third signal being related to the second signal.The fourth signal is associated with a primary current flowing through aprimary winding of the power converter. Moreover, the method includesprocessing information associated with the third signal and the fourthsignal, generating a second comparison signal based on at leastinformation associated with the third signal and the fourth signal,receiving at least the second comparison signal, processing informationassociated with the second comparison signal, and generating a logicsignal based on at least information associated with the secondcomparison signal. Also, the method includes receiving at least thefirst comparison signal and the logic signal, generating a modulationsignal based on at least information associated with the firstcomparison signal and the logic signal, receiving the modulation signal,and outputting a drive signal based on at least information associatedwith the modulation signal to adjust the primary current.

According to yet another embodiment, a system for regulating a powerconverter includes a first comparator configured to receive a firstsignal and a second signal and generate a first comparison signal basedon at least information associated with the first signal and the secondsignal, and the first signal is associated with at least an outputcurrent of a power converter. Additionally, the system includes a secondcomparator configured to receive a third signal and a fourth signal andgenerate a second comparison signal based on at least informationassociated with the third signal and the fourth signal. The third signalis related to the second signal, and the fourth signal is associatedwith a primary current flowing through a primary winding of the powerconverter. Moreover, the system includes a logic component configured toreceive at least the second comparison signal and generate a logicsignal based on at least information associated with the secondcomparison signal, and a pulse-width-modulation generator configured toreceive at least the first comparison signal and the logic signal andgenerate a modulation signal based on at least information associatedwith the first comparison signal and the logic signal. The modulationsignal is associated with a modulation frequency. Also, the systemincludes a driver component configured to receive the modulation signaland output a drive signal to a switch to adjust the primary current.Also, the system includes a first current generator configured toreceive the modulation signal and output a compensation current based onat least information associated with the modulation frequency togenerate a compensation voltage and adjust the first signal, and asecond current generator configured to receive the modulation signalassociated with the modulation frequency and output an offset currentbased on at least information associated with the modulation frequencyto generate an offset voltage and adjust the fourth signal.

According to yet another embodiment, a method for regulating a powerconverter includes receiving a first signal and a second signal. Thefirst signal is associated with at least an output current of a powerconverter. Additionally, the method includes processing informationassociated with the first signal and the second signal, generating afirst comparison signal based on at least information associated withthe first signal and the second signal, and receiving a third signal anda fourth signal, the third signal being related to the second signal.The fourth signal is associated with a primary current flowing through aprimary winding of the power converter. Moreover, the method includesprocessing information associated with the third signal and the fourthsignal, generating a second comparison signal based on at leastinformation associated with the third signal and the fourth signal,receiving at least the second comparison signal, processing informationassociated with the second comparison signal, and generating a logicsignal based on at least information associated with the secondcomparison signal. Also, the method includes receiving at least thefirst comparison signal and the logic signal, and generating amodulation signal based on at least information associated with thefirst comparison signal and the logic signal. The modulation signal isassociated with a modulation frequency. Additionally, the methodincludes receiving the modulation signal, outputting a drive signalbased on at least information associated with the modulation signal toadjust the primary current, outputting a compensation current based onat least information associated with the modulation frequency togenerate a compensation voltage and adjust the first signal, andoutputting an offset current based on at least information associatedwith the modulation frequency to generate an offset voltage and adjustthe fourth signal.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system with primary-side sensing and regulation.

FIG. 2 is a simplified diagram showing a conventional operationmechanism for the flyback power conversion system 100.

FIG. 3A and FIG. 3B are simplified diagrams showing switching frequencyand peak current as functions of output current of a power conversionsystem in the constant-voltage (CV) mode according to an embodiment ofthe present invention.

FIG. 4 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent according to an embodiment of the present invention.

FIG. 5 is a simplified timing diagram for the switch-mode powerconversion system 400 with constant voltage control according to anembodiment of the present invention.

FIG. 6 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent according to another embodiment of the present invention.

FIG. 7 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent with voltage compensation according to yet another embodiment ofthe present invention.

FIG. 8 is a simplified diagram showing a compensation current generatorfor the power conversion system 700 according to an embodiment of thepresent invention.

FIG. 9 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent with offset modulation current according to yet anotherembodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides switching frequency and peakcurrent adjustments in response to loading changes. Merely by way ofexample, the invention has been applied to a flyback power converter.But it would be recognized that the invention has a much broader rangeof applicability.

Referring to FIGS. 1 and 2, information about the output voltage of thepower conversion system 100 often is sampled only once every switchingperiod. The switching period is inversely proportional to the switchingfrequency, which usually is set low at no load or light load conditionsto reduce power consumption. But the low switching frequency often leadsto poor dynamic response for the power conversion system 100 if the loadchanges from no load or light load to full load. For example, if theswitching frequency is several hundred Hz at no load or light loadconditions, information about the output voltage of the power conversionsystem 100 is sampled once every several msec. If the load changes fromno load or light load to full load (e.g., the output current changing to1 A at full load), the output voltage may drop below an acceptablelevel, because the controller does not respond until the next samplingis performed after, for example, several msec. One way to solve thisproblem is to increase the switching frequency at no load or light loadconditions. But if the switching frequency is increased, the peakcurrent of the primary winding at no load or light load conditionsshould be limited such that the output voltage does not exceed anacceptable level.

FIG. 3A and FIG. 3B are simplified diagrams showing switching frequencyand peak current as functions of output current of a power conversionsystem in the constant-voltage (CV) mode according to an embodiment ofthe present invention. These diagrams are merely examples, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The curve 310 represents the switching frequency (e.g., F_(sw)) as afunction of output current (e.g., I_(out)), and the curve 320 representsthe peak current (e.g., I_(peak)) for primary winding as a function ofoutput current (e.g., the I_(out)). For example, if I_(out)=I₁, thepower conversion system is at no load conditions, and if I_(out)=I₆, thepower conversion system is at full load conditions. In another example,I₁<I₂<I₃<I₄<I₅<I₆.

As shown in FIG. 3A, the switching frequency (e.g., F_(sw)) changes withthe output current (e.g., I_(out)) at a slope S_(1f) if I₁≤I_(out)<I₂,at a slope S_(2f) if I₂≤I_(out)<I₅, and at a slope S_(3f) ifI₅≤I_(out)I₆ according to one embodiment. For example, each of theslopes S_(1f), S_(2f), and S_(3f) is larger than zero.

As shown in FIG. 3B, the peak current (e.g., I_(peak)) for eachswitching period (e.g., T_(sw)) changes with the output current (e.g.,I_(out)) at a slope S_(1p) if I₁≤I_(out)<I₃, at a slope S_(2p) ifI₃≤I_(out)<I₄, and at a slope S_(3p) if I₄≤I_(out)<I₆ according toanother embodiment. For example, the slopes S_(1p) and S_(3p) each areequal to or larger than zero. In another example, the slope S_(2p) islarger than zero. According to yet another embodiment, the powerconversion system operates with pulse-frequency modulation forI₁≤I_(out)<I₃, with both pulse-frequency modulation and pulse-widthmodulation for I₃≤I_(out)<I₄, and with pulse-frequency modulation forI₄≤I_(out)<I₆. For example, the slopes S_(1p) and S_(3p) each are equalto zero, and the peak current (e.g., I_(peak)) increases from I_(min) toI_(max) at the slope S_(2p).

FIG. 4 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The power conversion system 400 includes a primary winding 1410, asecondary winding 1412, an auxiliary winding 1414, a switch 1420 (e.g.,a bipolar transistor), a current sensing resistor 1430, an equivalentresistor 1440 for an output cable, resistors 1450 and 1452, and arectifying diode 1460. Additionally, the power conversion system 400also includes a demagnetization detector 420, a sampling controller 422,a sampling switch 424, a capacitor 426, an oscillator 428, an erroramplifier 430, an exponential generator 440, a comparator 450, aflip-flop component 452, a gate driver 454, comparators 460, 462, and464, a logic component 466, resistors 470 and 472, and a capacitor 474.

For example, the primary winding 1410, the secondary winding 1412, theauxiliary winding 1414, the switch 1420, the current sensing resistor1430, the equivalent resistor 1440, the resistors 1450 and 1452, and therectifying diode 1460 are the same as the primary winding 110, thesecondary winding 112, the auxiliary winding 114, the switch 120, thecurrent sensing resistor 130, the equivalent resistor 140, the resistors150 and 152, and the rectifying diode 160, respectively. In anotherexample, the demagnetization detector 420, the sampling controller 422,the sampling switch 424, the capacitor 426, the oscillator 428, theerror amplifier 430, the exponential generator 440, the comparator 450,the flip-flop component 452, the gate driver 454, the comparators 460,462, and 464, the logic component 466, the resistors 470 and 472, andthe capacitor 474 are located on a chip 410. In yet another example, thechip 410 includes terminals 412, 414, and 416.

FIG. 5 is a simplified timing diagram for the switch-mode powerconversion system 400 with constant voltage control according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications.

As shown in FIG. 5, the waveform 510 represents turned-on and turned-offconditions of the switch 1420 as a function of time, the waveform 520represents a ramping signal (e.g., V_(ramp)) as a function of time, thewaveform 530 represents an amplified signal 431 (e.g., Y_(ea)) as afunction of time, and the waveform 540 represents a feedback signal 1455as a function of time. Additionally, the waveform 550 represents asensed signal 461 (e.g., V_(cs)) as a function of time, the waveform 552represents a control signal 475 (e.g., V_(p)) as a function of time, andthe waveform 554 represents a threshold signal 473 (e.g., V_(th) _(_)_(max)) as a function of time.

As shown in FIGS. 4 and 5, information about the output voltage isextracted through the auxiliary winding 1414 according to oneembodiment. For example, the auxiliary winding 1414, together with theresistors 1450 and 1452, generates the feedback signal 1455 (e.g.,V_(FB) corresponding to the waveform 540) at a node 1454. In anotherexample, the feedback signal 1455 (e.g., V_(FB)) is received by at leastthe demagnetization detector 420 and the sampling switch 424.

In response, the demagnetization detector 420 outputs a signal 421 tothe exponential generator 440 according to one embodiment. For example,the oscillator 428 also outputs a clock signal 429 to the exponentialgenerator 440. In another example, the exponential generator 440generates the ramping signal 441 (e.g., V_(ramp) corresponding to thewaveform 520) as follows:

$\begin{matrix}{{V_{ramp}(n)} = {{\left( {V_{refb} - V_{refa}} \right) \times e^{- {(\frac{n \times T}{\tau})}}} + V_{refa}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

where V_(ramp) represents the voltage magnitude of the ramping signal441. Additionally, V_(refa) and V_(refb) each represent a constantvoltage level. For example, V_(refa) equals 1V, and V_(refb) equals 3V.Moreover, n represents the time for the ramping signal 441 to fall fromV_(refb) since the last reset of the ramping signal 441 in terms of thenumber of the clock periods. T is the clock period of the clock signal429. Furthermore, T is the time constant. Specifically, if 0≤n≤64,τ=128×T; if 64<n≤128, τ=256×T; if 128<n≤256, τ=512×T; and if 256<n≤512,τ=1024×T.

In one embodiment, when the switch 1420 is turned off, the energy storedin the transformer is released to the output terminal. For example, thedemagnetization process starts, and the current flowing through thesecondary winding 1412 ramps down linearly. For example, when thedemagnetization process almost ends and the current flowing through thesecondary winding 1412 approaches zero, a sampling signal 423 isgenerated by the sampling controller 422 to sample the feedback signal1455 (e.g., V_(FB) corresponding to the waveform 540) by closing thesampling switch 424. In another example, after the sampling process iscompleted, the sampling switch 424 is open in response to the samplingsignal 423. In yet another example, the sampled voltage is held on thecapacitor 426, and compared with a reference voltage V_(ref), such as2V.

The difference between the sampled/held voltage and the referencevoltage V_(ref) is amplified by the error amplifier 430 to generate theamplified signal 431 (e.g., V_(ea) correspond to the waveform 530)according to an embodiment. According to another embodiment, theamplified signal 431 is received by the resistor 470 and the negativeinput terminal of the comparator 450. For example, the resistor 470,together with the resistor 472 and the capacitor 474, outputs thecontrol signal 475 (e.g., V_(p) corresponding to the waveform 552) tothe comparator 460. In another example, the resistors 470 and 472 andthe capacitor 474 form a compensation network, which perform attenuationand low-pass filtering to the amplified signal 431 and generates thecontrol signal 475. In yet another example, the comparator 450 alsoreceives the ramping signal 441 (e.g., V_(ramp) corresponding to thewaveform 520) at the positive input terminal, and in response sends anoutput signal 451 to the flip-flop component 452.

As shown in FIG. 5, when the demagnetization process starts, the rampingsignal 441 (e.g., V_(ramp) corresponding to the waveform 520) isrestored to an initial value (e.g., V_(refb)), but after thedemagnetization process is completed, the ramping signal 441 decreasesexponentially according to one embodiment. In another embodiment, if theramping signal 441 becomes smaller than the amplified signal 431 (e.g.,Y_(ea) corresponding to the waveform 530) in magnitude, the comparisonsignal 451 changes to the logic low level, causing the signal 453 tochange to the logic high level and causing the switch 1420 to be turnedon.

In another embodiment, a primary current 1411 that flows through theprimary winding 1410 is sensed by the current sensing resistor 1430,which in response outputs the sensed signal 461 (e.g., V_(cs)corresponding to the waveform 550) to the comparators 460, 462, and 464.For example, if the switch 1420 is closed (e.g., being turned on), thetransformer stores energy and the primary current 1411 ramps uplinearly, causing the sensed signal 461 (e.g., V_(cs)) to also ramp uplinearly. In another example, the positive terminal of the comparator460 receives the control signal 475 (e.g., V_(p) corresponding to thewaveform 552), and the negative terminal of the comparator 460 receivesthe sensed signal 461. In another example, the positive terminal of thecomparator 462 receives the threshold signal 463 (e.g., V_(th) _(_)_(max) corresponding to the waveform 554), and the negative terminal ofthe comparator 462 receives the sensed signal 461. In yet anotherexample, the positive terminal of the comparator 464 receives the sensedsignal 461, and the negative terminal of the comparator 464 receives athreshold signal 465 (e.g., V_(th) _(_) _(min) which is smaller thanV_(th) _(_) _(max) in magnitude).

In yet another embodiment, the comparators 460, 462, and 464 generatecomparison signals 471, 473, and 479 respectively, all of which arereceived by the logic component 466. For example, the logic component466 in response generates a logic signal 467.

According to one embodiment, the flip-flop component 452 receives thecomparison signal 451 and the logic signal 467, and in responsegenerates a signal 453. For example, as shown in FIG. 5, if thecomparison signal 451 is at the logic low level but the logic signal 467is at the logic high level, the signal 453 is at the logic high level,and if the comparison signal 451 is at the logic low level and the logicsignal 467 is also at the logic low level, the signal 453 is at thelogic low level. In another example, if the logic signal 467 is at thelogic low level, the signal 453 from the Q terminal is also at the logiclow level in order to turn off the switch 1420, regardless of whetherthe comparison signal 451 is at the logic high level or at the logic lowlevel. In yet another example, if the logic signal 467 is at the logichigh level and the comparison signal 451 is at the logic low level, thesignal 453 is at the logic high level to turn on the switch 1420.

According to another embodiment, the signal 453 is received by the gatedriver 454, which outputs a drive signal 455 to the switch 1420 throughthe terminal 412 (e.g., outputting the base current 455 to the bipolartransistor 1420 through the terminal 412). For example, if the signal453 is at the logic high level, the drive signal 455 causes the switch1420 to be closed (e.g., being turned on as shown by the waveform 510).In another example, if the signal 453 is at the logic low level, thedrive signal 455 causes the switch 1420 to be open (e.g., being turnedoff as shown by the waveform 510).

As shown in FIGS. 4 and 5, the larger the output loading (e.g., theoutput current) is, the larger the amplified signal 431 (e.g., V_(ea)corresponding to the waveform 530) becomes, causing the off-time (e.g.,T_(off)) of the switch 1420 to become shorter and the switchingfrequency (e.g., F_(sw)) to become higher according to one embodiment.According to another embodiment, the smaller the output loading (e.g.,the output current) is, the smaller the amplified signal 431 (e.g.,V_(ea) corresponding to the waveform 530) becomes, causing the off-time(e.g., T_(off)) of the switch 1420 to become longer and the switchingfrequency (e.g., F_(sw)) to become lower as shown in FIG. 3A.

According to yet another embodiment, the logic component 466 includes anOR gate and other components. For example, if the control signal 475(e.g. V_(p)) is smaller than the threshold signal 465 (e.g., V_(th) _(_)_(min)) in magnitude, the peak magnitude of the sensed signal 461 (e.g.,V_(cs) corresponding the waveform 550) is limited to the magnitude ofthe threshold signal 465 (e.g., V_(th) _(_) _(min) corresponding to thewaveform 556), and the on-time of the switch 1420 (e.g., T_(on)) and thepeak magnitude of the primary current 1411 remains constant regardlessof the output loading (e.g., the output current) as shown forI₁≤I_(out)<I₃ in FIG. 3B.

In another example, if the control signal 475 (e.g., V_(p)) is largerthan the threshold signal 465 (e.g., V_(th) _(_) _(min)) but smallerthan the threshold signal 463 (e.g., V_(th) _(_) _(max)) in magnitude,the peak magnitude of the sensed signal 461 (e.g., V_(cs) correspondingthe waveform 550) is limited to the magnitude of the control signal 475(e.g., V_(p) corresponding to the waveform 552). For example, thecontrol signal 475 (e.g., V_(p)) increases with the output loading(e.g., the output current) in magnitude; hence both the on-time of theswitch 1420 (e.g., T_(on)) and the peak magnitude of the primary current1411 increases with the output loading (e.g., the output current) asshown for I₃≤I_(out)<I₄ in FIG. 3B.

In yet another example, if the control signal 475 (e.g., V_(p)) becomeslarger than the threshold signal 463 (e.g., V_(th) _(_) _(max)) inmagnitude, the peak magnitude of the sensed signal 461 (e.g., V_(cs)corresponding the waveform 550) is limited to the magnitude of thethreshold signal 463 (e.g., V_(th) _(_) _(max) corresponding to thewaveform 554). For example, both the on-time of the switch 1420 (e.g.,T_(on)) and the peak magnitude of the primary current 1411 remainsconstant regardless of the output loading (e.g., the output current) asshown for I₄≤I_(out)<I₆ in FIG. 3B.

As discussed above and further emphasized here, FIG. 4 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the bipolar transistor 1420 is replacedby a MOS transistor as shown in FIG. 6.

FIG. 6 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent according to another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The power conversion system 600 includes a primary winding 1610, asecondary winding 1612, an auxiliary winding 1614, a switch 1620 (e.g.,a MOS transistor), a current sensing resistor 1630, an equivalentresistor 1640 for an output cable, resistors 1650 and 1652, and arectifying diode 1660. Additionally, the power conversion system 600also includes a demagnetization detector 620, a sampling controller 622,a sampling switch 624, a capacitor 626, an oscillator 628, an erroramplifier 630, an exponential generator 640, a comparator 650, aflip-flop component 652, a gate driver 654, comparators 660, 662, and664, a logic component 666, resistors 670 and 672, and a capacitor 674.

For example, the primary winding 1610, the secondary winding 1612, theauxiliary winding 1614, the switch 1620, the current sensing resistor1630, the equivalent resistor 1640, the resistors 1650 and 1652, and therectifying diode 1660 are the same as the primary winding 110, thesecondary winding 112, the auxiliary winding 114, the switch 120, thecurrent sensing resistor 130, the equivalent resistor 140, the resistors150 and 152, and the rectifying diode 160, respectively. In anotherexample, the demagnetization detector 620, the sampling controller 622,the sampling switch 624, the capacitor 626, the oscillator 628, theerror amplifier 630, the exponential generator 640, the comparator 650,the flip-flop component 652, the gate driver 654, the comparators 660,662, and 664, the logic component 666, the resistors 670 and 672, andthe capacitor 674 are located on a chip 610. In yet another example, thechip 610 includes terminals 612, 614, and 616.

In yet another example, the demagnetization detector 620, the samplingcontroller 622, the sampling switch 624, the capacitor 626, theoscillator 628, the error amplifier 630, the exponential generator 640,the comparator 650, the flip-flop component 652, the gate driver 654,the comparators 660, 662, and 664, the logic component 666, theresistors 670 and 672, and the capacitor 674 are similar to thedemagnetization detector 420, the sampling controller 422, the samplingswitch 424, the capacitor 426, the oscillator 428, the error amplifier430, the exponential generator 440, the comparator 450, the flip-flopcomponent 452, the gate driver 454, the comparators 460, 462, and 464,the logic component 466, the resistors 470 and 472, and the capacitor474, respectively, except that certain modifications are made in orderto drive a MOS transistor instead of a bipolar transistor. In yetanother example, the auxiliary winding 1614, together with the resistors1650 and 1652, generates a feedback signal 1655 at a node 1654.

FIG. 7 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent with voltage compensation according to yet another embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.

The power conversion system 700 includes the primary winding 1410, thesecondary winding 1412, the auxiliary winding 1414, the switch 1420(e.g., a bipolar transistor), the current sensing resistor 1430, theequivalent resistor 1440 for the output cable, the resistors 1450 and1452, and the rectifying diode 1460. Additionally, the power conversionsystem 700 also includes the demagnetization detector 420, the samplingcontroller 422, the sampling switch 424, the capacitor 426, theoscillator 428, the error amplifier 430, the exponential generator 440,the comparator 450, the flip-flop component 452, the gate driver 454,the comparators 460, 462, and 464, the logic component 466, theresistors 470 and 472, and the capacitor 474. Moreover, the powerconversion system 700 also includes a frequency computation component720, a frequency-to-current converter 730, and a current generationcomponent 740.

For example, the demagnetization detector 420, the sampling controller422, the sampling switch 424, the capacitor 426, the oscillator 428, theerror amplifier 430, the exponential generator 440, the comparator 450,the flip-flop component 452, the gate driver 454, the comparators 460,462, and 464, the logic component 466, the resistors 470 and 472, thecapacitor 474, the frequency computation component 720, thefrequency-to-current converter 730, and the current generation component740 are located on a chip 710. In another example, the chip 710 includesterminals 712, 714, and 716. In yet another example, the frequencycomputation component 720, the frequency-to-current converter 730, andthe current generation component 740 are parts of a compensation currentgenerator.

According to one embodiment, the switching frequency increases with theoutput loading (e.g., the output current) and thus reflects themagnitude of the output loading (e.g., the magnitude of the outputcurrent) for at least I₂≤I_(out)<I₅ as shown in FIG. 3A. For example,the frequency computation component 720 receives the output signal ofthe flip-flop component 452, which is also received by the gate driver454, and generates a frequency signal 721 that represents the magnitudeof the switching frequency. In another example, the frequency signal 721is received by the frequency-to-current converter 730 and is convertedto a current signal 731. In yet another example, the current generationcomponent 740 receives the current signal 731 and in response generatesa compensation current 741 (e.g., I_(comp)). In yet another example, thecurrent generation component 740 also includes a low-pass filter tosmooth out the compensation current 741 (e.g., I_(comp)).

According to another embodiment, the compensation current 741 (e.g.,I_(comp)) flows out of the chip 710 through the terminal 716, andgenerates a compensation voltage as follows:

$\begin{matrix}{V_{comp} = {\frac{R_{1} \times R_{2}}{R_{1} \times R_{2}} \times I_{comp}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

where V_(comp) represents the compensation voltage, and I_(comp)represents the compensation current 741. Additionally, R₁ and R₂represent resistance values of the resistors 1450 and 1452,respectively. For example, the compensation voltage is used tocompensate for the voltage-drop due to the output cable (which isrepresented by the equivalent resistor 1440), and is also compensatedfor the output-voltage error due to cross regulation of the secondarywinding and the auxiliary winding at no load and light load conditions.In another example, the compensation voltage is used to adjust thefeedback signal 1455.

FIG. 8 is a simplified diagram showing a compensation current generatorfor the power conversion system 700 according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications.

The compensation current generator includes the comparators 1110 and1112, the flip-flop component 1120, the signal generator 1130, theflip-flop components 1140, the encoding component 1150, the AND gate1160, the switches 1170, the current sinks 1172, and the current source1174. Additionally, the compensation current generator also includestransistors 1280, 1282, 1284, and 1286, a resistor 1290, and a capacitor1292, an exponential generator 1010 and a frequency computationcomponent 1014. U.S. patent application Ser. No. 12/859,138 isincorporated by reference herein for all purposes.

As shown in FIG. 8, the compensation current 741 that is dependent onthe switching frequency is generated according to one embodiment. Forexample, since higher switching frequencies correspond to heavierloading conditions (e.g., larger output currents), and lower switchingfrequencies correspond to no load or light load conditions (e.g.,smaller output currents); a larger compensation current is generated forlower switching frequency and a smaller compensation current isgenerated for higher switching frequency. In another example, thecompensation current 741 is smoothed out by a low-pass filter that isformed by the resistor 1290 and the capacitor 1292. In yet anotherexample, the compensation current 741 flows out of the chip 710 throughthe terminal 716, and together with the resistors 1450 and 1452generates the compensation voltage (e.g., V_(comp)) that is superimposedwith the feedback signal.

As discussed above and further emphasized here, FIG. 7 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the bipolar transistor 1420 is replacedby a MOS transistor, and one or more components of the power conversionsystem 700 are modified in order to drive the MOS transistor instead ofa bipolar transistor.

FIG. 9 is a simplified diagram showing a power conversion system thatadjusts switching frequency and peak current in response to outputcurrent with offset modulation current according to yet anotherembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications.

The power conversion system 900 includes a primary winding 1910, asecondary winding 1912, an auxiliary winding 1914, a switch 1920 (e.g.,a bipolar transistor), a current sensing resistor 1930, an equivalentresistor 1940 for an output cable, resistors 1950 and 1952, and arectifying diode 1960. Additionally, the power conversion system 900also includes the demagnetization detector 920, the sampling controller922, the sampling switch 924, the capacitor 926, the oscillator 928, theerror amplifier 930, the exponential generator 940, the comparator 950,the flip-flop component 952, and the gate driver 954. Moreover, thepower conversion system 900 also includes a frequency computationcomponent 1720, a frequency-to-current converter 1730, and a currentgeneration component 1740. Also, the power conversion system 900includes a comparator 960, a frequency-to-current converter 1750, acurrent generation component 1760, and a resistor 1932.

For example, the primary winding 1910, the secondary winding 1912, theauxiliary winding 1914, the switch 1920, the current sensing resistor1930, the equivalent resistor 1940, the resistors 1950 and 1952, and therectifying diode 1960 are the same as the primary winding 110, thesecondary winding 112, the auxiliary winding 114, the switch 120, thecurrent sensing resistor 130, the equivalent resistor 140, the resistors150 and 152, and the rectifying diode 160, respectively. In anotherexample, the demagnetization detector 920, the sampling controller 922,the sampling switch 924, the capacitor 926, the oscillator 928, theerror amplifier 930, the exponential generator 940, the comparator 950,the flip-flop component 952, the gate driver 954, the frequencycomputation component 1720, the frequency-to-current converter 1730, thecurrent generation component 1740, the comparator 960, thefrequency-to-current converter 1750, and the current generationcomponent 1760 are located on a chip 910. In another example, theauxiliary winding 1914, together with the resistors 1950 and 1952,generates a feedback signal 1955 at a node 1954. In another example, thechip 910 includes terminals 912, 914, and 916.

In yet another example, the demagnetization detector 920, the samplingcontroller 922, the sampling switch 924, the capacitor 926, theoscillator 928, the error amplifier 930, the exponential generator 940,the comparator 950, the flip-flop component 952, the gate driver 954,the frequency computation component 1720, the frequency-to-currentconverter 1730, and the current generation component 1740 aresubstantially the same as the demagnetization detector 420, the samplingcontroller 422, the sampling switch 424, the capacitor 426, theoscillator 428, the error amplifier 430, the exponential generator 440,the comparator 450, the flip-flop component 452, the gate driver 454,the frequency computation component 720, the frequency-to-currentconverter 730, and the current generation component 740, respectively.

According to one embodiment, the switching frequency increases with theoutput loading (e.g., the output current) and thus reflects themagnitude of the output loading (e.g., the magnitude of the outputcurrent) in at least region II of FIG. 3A. For example, the frequencycomputation component 1720 receives the output signal of the flip-flopcomponent 952, which is also received by the gate driver 954, andgenerates a frequency signal 1721 that represents the magnitude of theswitching frequency. In another example, the frequency signal 1721 isreceived by the frequency-to-current converters 1730 and 1750 and isconverted to current signals 1731 and 1751, respectively.

As shown in FIG. 9, the current generation component 1740 receives thecurrent signal 1731 and in response generates a compensation current1741 (e.g., I_(comp)), and the current generation component 1760receives the current signal 1751 and in response generates an offsetmodulation current 1761 (e.g., I_(offset)) according to one embodiment.For example, the offset modulation current 1761 (e.g., I_(offset))decreases with increasing switching frequency and thus also decreaseswith increasing output loading (e.g., with increasing output current).

According to another embodiment, the offset modulation current 1761(e.g., I_(offset)) flows out of the chip 910 through the terminal 914,and generates an offset voltage as follows:

V _(offset) =R _(c) ×I _(offset)  (Equation 7)

where V_(offset) represents the offset voltage, and I_(offset)represents the offset modulation current 1761. Additionally, R_(c)represents the resistance value of the resistor 1932.

For example, the offset voltage is used to adjust a sensed signal 963(e.g., V_(cs)). In another example, using Equation 7, the peak magnitudeof a primary current 1911 that flows through the primary winding 1912 isdetermined as follows:

$\begin{matrix}{I_{peak} = \frac{V_{th\_ OC} - {R_{c} \times I_{offset}}}{R_{s}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

where I_(peak) represents the peak magnitude of the primary current1911, and V_(th) _(_) _(OC) represents the threshold signal 961.Additionally, R_(c) represents the resistance value of the resistor1932. For example, the offset modulation current 1761 (e.g., I_(offset))decreases with increasing output loading (e.g., with increasing outputcurrent); hence the peak magnitude of the primary current 1911 increaseswith increasing output loading (e.g., with increasing output current)but cannot exceed V_(th) _(_) _(OC)/R_(s) according to Equation 8.

As shown in FIG. 9, the compensation current 1741 (e.g., I_(comp)) isgenerated by at least the frequency-to-current converter 1730 and thecurrent generation component 1740, and the offset modulation current1761 (e.g., I_(offset)) is generated by at least thefrequency-to-current converter 1750 and the current generation component1760 according to some embodiments. For example, the compensationcurrent 1741 (e.g., I_(comp)) and the offset modulation current 1761(e.g., I_(offset)) are different and separate, even though both thecurrents 1741 and 1761 are derived from the frequency signal 1721 thatis generated by the frequency computation component 1720.

As discussed above and further emphasized here, FIG. 9 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the bipolar transistor 1920 is replacedby a MOS transistor, and one or more components of the power conversionsystem 900 are modified in order to drive the MOS transistor instead ofa bipolar transistor. In another example, the current generationcomponents 1740 and 1760 each include a low-pass filter. In yet anotherexample, the current generation components 1740 and 1760 share alow-pass filter that is used to smooth out both the compensation current1741 (e.g., I_(comp)) and the offset modulation current 1761 (e.g.,I_(offset)).

According to another embodiment, a system for regulating a powerconverter includes a comparator configured to receive a first signal anda second signal and generate a comparison signal based on at leastinformation associated with the first signal and the second signal. Thefirst signal is associated with at least an output current of a powerconverter. Additionally, the system includes a pulse-width-modulationgenerator configured to receive at least the comparison signal andgenerate a modulation signal based on at least information associatedwith the comparison signal, and a driver component configured to receivethe modulation signal and output a drive signal to a switch to adjust aprimary current flowing through a primary winding of the powerconverter. The modulation signal is associated with a modulationfrequency corresponding to a modulation period. The modulation frequencyincreases with the output current at a first slope within a firstcurrent range, the modulation frequency increases with the outputcurrent at a second slope within a second current range, and themodulation frequency increases with the output current at a third slopewithin a third current range. The first current range and the thirdcurrent range are separated by at least the second current range, andeach of the first slope, the second slope, and the third slope is largerthan zero. The primary current is associated with a peak magnitude foreach modulation period. The peak magnitude remains constant or increaseswith respect to the output current at a fourth slope within a fourthcurrent range, and the fourth slope is equal to or larger than zero. Thepeak magnitude increases with the output current at a fifth slope withina fifth current range, and the fifth slope is larger than zero. The peakmagnitude remains constant or increases with respect to the outputcurrent at a sixth slope within a sixth current range, and the sixthslope is equal to or larger than zero. The fourth current range and thesixth current range are separated by at least the fifth current range.For example, the system is implemented according to FIG. 4, FIG. 6, FIG.7, and/or FIG. 9.

According to another embodiment, a method for regulating a powerconverter includes receiving a first signal and a second signal. Thefirst signal is associated with at least an output current of a powerconverter. Additionally, the method includes processing informationassociated with the first signal and the second signal, generating acomparison signal based on at least information associated with thefirst signal and the second signal, receiving at least the comparisonsignal, and generating a modulation signal based on at least informationassociated with the comparison signal. Moreover, the method includesreceiving the modulation signal, and outputting a drive signal based onat least at least information associated with the modulation signal toadjust a primary current flowing through a primary winding of the powerconverter. The modulation signal is associated with a modulationfrequency corresponding to a modulation period. The modulation frequencyincreases with the output current at a first slope within a firstcurrent range, the modulation frequency increases with the outputcurrent at a second slope within a second current range, and themodulation frequency increases with the output current at a third slopewithin a third current range. The first current range and the thirdcurrent range are separated by at least the second current range, andeach of the first slope, the second slope, and the third slope is largerthan zero. The primary current is associated with a peak magnitude foreach modulation period. The peak magnitude remains constant or increaseswith respect to the output current at a fourth slope within a fourthcurrent range, and the fourth slope is equal to or larger than zero. Thepeak magnitude increases with the output current at a fifth slope withina fifth current range, and the fifth slope is larger than zero. The peakmagnitude remains constant or increases with respect to the outputcurrent at a sixth slope within a sixth current range, and the sixthslope is equal to or larger than zero. The fourth current range and thesixth current range are separated by at least the fifth current range.For example, the method is implemented according to FIG. 4, FIG. 6, FIG.7, and/or FIG. 9.

According to yet another embodiment, a system for regulating a powerconverter includes a first comparator configured to receive a firstsignal and a second signal and generate a first comparison signal basedon at least information associated with the first signal and the secondsignal. The first signal is associated with at least an output currentof a power converter. Additionally, the system includes a secondcomparator configured to receive a third signal and a fourth signal andgenerate a second comparison signal based on at least informationassociated with the third signal and the fourth signal. The third signalis related to the second signal, and the fourth signal is associatedwith a primary current flowing through a primary winding of the powerconverter. Moreover, the system includes a logic component configured toreceive at least the second comparison signal and generate a logicsignal based on at least information associated with the secondcomparison signal, a pulse-width-modulation generator configured toreceive at least the first comparison signal and the logic signal andgenerate a modulation signal based on at least information associatedwith the first comparison signal and the logic signal, and a drivercomponent configured to receive the modulation signal and output a drivesignal to a switch to adjust the primary current. For example, thesystem is implemented according to FIG. 4, FIG. 6, and/or FIG. 7.

According to yet another embodiment, a method for regulating a powerconverter includes receiving a first signal and a second signal, and thefirst signal is associated with at least an output current of a powerconverter. Additionally, the method includes processing informationassociated with the first signal and the second signal, generating afirst comparison signal based on at least information associated withthe first signal and the second signal, and receiving a third signal anda fourth signal, the third signal being related to the second signal.The fourth signal is associated with a primary current flowing through aprimary winding of the power converter. Moreover, the method includesprocessing information associated with the third signal and the fourthsignal, generating a second comparison signal based on at leastinformation associated with the third signal and the fourth signal,receiving at least the second comparison signal, processing informationassociated with the second comparison signal, and generating a logicsignal based on at least information associated with the secondcomparison signal. Also, the method includes receiving at least thefirst comparison signal and the logic signal, generating a modulationsignal based on at least information associated with the firstcomparison signal and the logic signal, receiving the modulation signal,and outputting a drive signal based on at least information associatedwith the modulation signal to adjust the primary current. For example,the method is implemented according to FIG. 4, FIG. 6, and/or FIG. 7.

According to yet another embodiment, a system for regulating a powerconverter includes a first comparator configured to receive a firstsignal and a second signal and generate a first comparison signal basedon at least information associated with the first signal and the secondsignal, and the first signal is associated with at least an outputcurrent of a power converter. Additionally, the system includes a secondcomparator configured to receive a third signal and a fourth signal andgenerate a second comparison signal based on at least informationassociated with the third signal and the fourth signal. The third signalis related to the second signal, and the fourth signal is associatedwith a primary current flowing through a primary winding of the powerconverter. Moreover, the system includes a logic component configured toreceive at least the second comparison signal and generate a logicsignal based on at least information associated with the secondcomparison signal, and a pulse-width-modulation generator configured toreceive at least the first comparison signal and the logic signal andgenerate a modulation signal based on at least information associatedwith the first comparison signal and the logic signal. The modulationsignal is associated with a modulation frequency. Also, the systemincludes a driver component configured to receive the modulation signaland output a drive signal to a switch to adjust the primary current.Also, the system includes a first current generator configured toreceive the modulation signal and output a compensation current based onat least information associated with the modulation frequency togenerate a compensation voltage and adjust the first signal, and asecond current generator configured to receive the modulation signalassociated with the modulation frequency and output an offset currentbased on at least information associated with the modulation frequencyto generate an offset voltage and adjust the fourth signal. For example,the system is implemented according to FIG. 9.

According to yet another embodiment, a method for regulating a powerconverter includes receiving a first signal and a second signal. Thefirst signal is associated with at least an output current of a powerconverter. Additionally, the method includes processing informationassociated with the first signal and the second signal, generating afirst comparison signal based on at least information associated withthe first signal and the second signal, and receiving a third signal anda fourth signal, the third signal being related to the second signal.The fourth signal is associated with a primary current flowing through aprimary winding of the power converter. Moreover, the method includesprocessing information associated with the third signal and the fourthsignal, generating a second comparison signal based on at leastinformation associated with the third signal and the fourth signal,receiving at least the second comparison signal, processing informationassociated with the second comparison signal, and generating a logicsignal based on at least information associated with the secondcomparison signal. Also, the method includes receiving at least thefirst comparison signal and the logic signal, and generating amodulation signal based on at least information associated with thefirst comparison signal and the logic signal. The modulation signal isassociated with a modulation frequency. Additionally, the methodincludes receiving the modulation signal, outputting a drive signalbased on at least information associated with the modulation signal toadjust the primary current, outputting a compensation current based onat least information associated with the modulation frequency togenerate a compensation voltage and adjust the first signal, andoutputting an offset current based on at least information associatedwith the modulation frequency to generate an offset voltage and adjustthe fourth signal. For example, the method is implemented according toFIG. 9.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1.-25. (canceled)
 26. An apparatus for a power converter, the apparatuscomprising: a first comparator configured to receive a first signal anda second signal and generate a first comparison signal based at least inpart on the first signal and the second signal, the first signal beingassociated with at least an output current of a power converter; asecond comparator configured to receive a third signal and a fourthsignal and generate a second comparison signal based at least in part onthe third signal and the fourth signal, the third signal being relatedto the first signal, the fourth signal being associated with a currentflowing through a primary winding of the power converter; and amodulation signal generator configured to receive the first comparisonsignal and the second comparison signal, generate a modulation signalbased at least in part on the first comparison signal and the secondcomparison signal, and output the modulation signal for adjusting thecurrent flowing through the primary winding of the power converter. 27.The apparatus of claim 26 and further comprising: a first resistorincluding a first resistor terminal and a second resistor terminal; asecond resistor including a third resistor terminal and a fourthresistor terminal; and a capacitor including a first capacitor terminaland a second capacitor terminal; wherein the second resistor terminal,the third resistor terminal, and the first capacitor terminal areconnected together; wherein: the first resistor is configured to receivethe first signal at the first resistor terminal; and the secondcomparator is further configured to receive the third signal from thefirst capacitor terminal.
 28. The apparatus of claim 27 wherein thesecond comparator is further configured to receive the third signal fromthe first capacitor terminal, the second resistor terminal, and thethird resistor terminal.
 29. The apparatus of claim 26 wherein themodulation signal generator includes an OR gate.
 30. The apparatus ofclaim 29 wherein the modulation signal generator further includes aflip-flop.
 31. The apparatus of claim 26 wherein the modulation signalgenerator includes a flip-flop.
 32. The apparatus of claim 26 whereinthe modulation signal generator is used to output a drive signal to aswitch, the switch being a bipolar transistor.
 33. The apparatus ofclaim 26 wherein the modulation signal generator is used to output adrive signal to a switch, the switch being a MOS transistor.
 34. Theapparatus of claim 26 and further comprising a current generatorconfigured to receive the modulation signal associated with a modulationfrequency and output a compensation current based on at leastinformation associated with the modulation frequency to generate acompensation voltage and adjust the first signal.
 35. The apparatus ofclaim 34 wherein the current generator includes: a frequency signalgenerator configured to receive the modulation signal and generate afrequency signal representing the modulation frequency based at least inpart on the modulation signal; a current converter configured to receivethe frequency signal and generate a current signal based on at leastinformation associate with the modulation frequency; and a currentgeneration component configured to receive the current signal and outputthe compensation current based at least in part on the current signal.36. The apparatus of claim 26 and further comprising a compensationnetwork configured to perform attenuation and low-pass filtering on thefirst signal and generate the third signal.
 37. The apparatus of claim26 and further comprising: a third comparator configured to receive thefourth signal and a first threshold signal and generate a thirdcomparison signal based at least in part on the fourth signal and thefirst threshold signal; and a fourth comparator configured to receivethe fourth signal and a second threshold signal and generate a fourthcomparison signal based at least in part on the fourth signal and thesecond threshold signal; wherein the modulation signal generator isfurther configured to receive the third comparison signal and the fourthcomparison signal and generate the modulation signal based at least inpart on the second comparison signal, the third comparison signal andthe fourth comparison signal.
 38. A method for a power converter, themethod comprising: receiving a first signal and a second signal, thefirst signal being associated with at least an output current of a powerconverter; generating a first comparison signal based at least in parton the first signal and the second signal; receiving a third signal anda fourth signal, the third signal being related to the first signal, thefourth signal being associated with a current flowing through a primarywinding of the power converter; generating a second comparison signalbased at least in part on the third signal and the fourth signal;receiving the first comparison signal and the second comparison signal;generating a modulation signal based at least in part on the firstcomparison signal and the second comparison signal; and outputting themodulation signal for adjusting the current flowing through the primarywinding of the power converter.
 39. The method of claim 38 and furthercomprising: processing information associated with the modulationsignal, the modulation signal being related to a modulation frequency;and outputting a compensation current based on at least informationassociated with the modulation frequency to generate a compensationvoltage and adjust the first signal.
 40. The method of claim 38 whereinthe receiving the first comparison signal and the second comparisonsignal includes receiving the first comparison signal, the secondcomparison signal, and two additional comparison signals.